The invention relates to a flame-retardant coating which forms an insulating layer and is based on substances which carbonize and which form a foam layer in the event of a fire, on film-forming binders, on blowing agents and on customary auxiliaries and additives.
Flame-retardant coatings which form an insulating layer, also called intumescent coatings, have the characteristic that they foam when exposed to the temperatures prevailing in the event of a fire, and this foaming of the abovementioned flame-retardant coating prevents, or at least hinders, the passage of heat to steel construction members, ceilings, walls, cables, pipes and the like.
U.S. Pat. No. 4,965,296 A1 describes a flame-retardant material composed of a flame-retardant coating material and of an electrically conductive material. This flame-retardant coating material is composed of substances which carbonize and which form foam, of a compound which produces gas, of a film-forming binder and of appropriate solvents. Customary other ingredients may be present if desired.
U.S. Pat. No. 4,879,320 describes a similar flame-retardant composition, but a ceramic fiber material has been added instead of a conductive material.
U.S. Pat. No. 5,225,464 describes an aqueous intumescence formulation based on a reaction product of phosphoric acid, melamine and monoammonium phosphate, which with pentaerythritol, with chlorinated hydrocarbons and with other compounds, in particular polyvinyl acetate, is intended to give an improved intumescence coating material.
DE 42 18 184 A1 describes an aqueous binder mixture composed of an aqueous solution and/or dispersion of a combination made from a) at least one NCO prepolymer which has urethane groups and blocked isocyanate groups and is soluble and/or dispersible in water in the presence of component b), and b) a polyamine component composed of at least one (cyclo)aliphatic polyamine having at least two primary and/or secondary amino groups.
Finally, DE 43 43 668 describes blowable flame-retardant coating compositions composed at least of
from 4 to 25% by weight of a film-forming binder,
from 10 to 4% by weight of ammonium polyphosphate,
from 8 to 40% by weight of at least one substance which carbonizes on exposure to heat,
from 6 to 25% by weight of a blowing agent,
from 0 to 5% by weight of dispersing agent, and
from 0 to 25% by weight of fillers.
A general disadvantage of the abovementioned flame-retardant coatings is that they contain halogen and/or have insufficient water resistance after drying.
The use of melamine as blowing agent is to be seen as particularly disadvantageous, since it reacts as a base in aqueous slurries. If, therefore, a flame-retardant coating which forms an insulating layer has a component which reacts as an acid in aqueous solution, the melamine is available as a reaction partner for this component. It is known that melamine and ammonium polyphosphate react in aqueous solution releasing ammonia (NH3). At increased temperature and increased atmospheric humidity this reaction can also take place in a dried flame-retardant coating which forms an insulating layer, thus reducing the flame-retardant properties of the coating.
The object of the present invention is therefore to provide flame-retardant coatings which form an insulating layer and which, without using melamine or, respectively, ammonium polyphosphate are water-resistant after drying and also release only extremely small amounts of NH3 at increased atmospheric humidity and increased temperature.
This object is achieved by a flame-retardant coating of the type described at the outset which forms an insulating layer, which comprises a melamine polyphosphate as blowing agent and as substance forming a foam layer.
The melamine polyphosphate preferably has the formula (HMPO3)n, where M is melamine and nxe2x89xa72, in particular from 2 to 10 000.
Melamine polyphosphate is a polymer made from melamine units and phosphate units which have been linked to give relatively short or relatively long chains. The distribution of the melamine units and phosphate units may be regular or irregular, and they may, if desired, also have been polymerized within themselves. Derivatives of melamine, such as melem, melam and others, may also be present.
The properties of the melamine polyphosphate may vary within certain limits, due to its different chain lengths and to the distribution and/or frequency of the melamine units and phosphate units.
Melamine polyphosphate is described in more detail in PCT/WO 98/45364, for example, where it is also described as melamine salt of polyphosphoric acid.
The polymeric chain here is composed of (HMPO3) units [where M is melamine] and
nxe2x89xa72, in particular from 5 to 10 000.
Melamine polyphosphate is usually obtained by heating melamine pyrophosphate under nitrogen at temperatures of 290xc2x0 C. and above to constant weight (PCT/WO 98/08898).
The novel flame-retardant coating which forms an insulating layer is preferably free from ammonium polyphosphate.
The novel flame-retardant coating which forms an insulating layer is preferably free from melamine and/or dicyandiamides.
The flame-retardant coating which forms an insulating layer preferably comprises
from 5 to 30 parts by weight of film-forming binder,
from 5 to 25 parts by weight of a substance which carbonizes,
from 30 to 70 parts by weight of melamine polyphosphate, and
from 10 to 50 parts by weight of customary auxiliaries and additives.
The flame-retardant coating which forms an insulating layer particularly preferably comprises
from 10 to 20 parts by weight of film-forming binder,
from 7 to 15 parts by weight of a substance which carbonizes,
from 40 to 60 parts by weight of melamine polyphosphate, and
from 20 to 40 parts by weight of customary auxiliaries and additives.
The flame-retardant coating which forms an insulating layer preferably comprises as film-forming binders
homopolymers based on vinyl acetate,
copolymers based on vinyl acetate, ethylene and vinyl chloride,
copolymers based on vinyl acetate and the vinyl ester of a long-chain branched carboxylic acid,
copolymers based on vinyl acetate and di-n-butyl maleate,
copolymers based on vinyl acetate and acrylates,
copolymers based on styrene and acrylates, and/or
copolymers based on acrylates,
vinyltoluene-acrylate copolymer,
styrene-acrylate copolymer,
vinyl-acrylate copolymer,
self-crosslinking polyurethane dispersions.
The substances which carbonize and are present in the flame-retardant coating which forms an insulating layer preferably comprise carbohydrates. The carbohydrates used preferably comprise pentaerythritol, dipentaerythritol, tripentaerythritol and/or polycondensates of pentaerythritol.
The auxiliaries or additives present in the flame-retardant coating which forms an insulating layer preferably comprise glass fibers, mineral fibers, kaolin, talc, aluminum oxide, aluminum hydroxide, magnesium hydroxide, precipitation silicas, silicates and/or pulverized celluloses.
The novel flame-retardant coating which forms an insulating layer is preferably halogen-free.
The novel flame-retardant coating which forms an insulating layer releases less than 100 ppm of NH3 when stored under high (atmospheric) moisture conditions (at up to 100% rel. humidity) and at increased temperature (about 75xc2x0 C.).
The novel flame-retardant coating (intumescence coating) in the form of a spreadable, sprayable or rollable coating agent, is used in protecting a very wide variety of substrates, preferably steel, wood, electrical cables or pipes.